Field of the Invention
The present invention relates to an image processing apparatus which performs image processing on a radiation image, an image processing method, and an image processing system.
Description of the Related Art
A radiation image obtained by irradiating an object with a radiation includes a component of primary radiation which travels straight from a radiation source and a component of a scattered ray which is a radiation scattered in the object, and further includes a noise component. Such a scattered-ray component may cause degradation of contrast of a radiation image. Furthermore, the noise component may cause degradation of image quality of the radiation image.
In recent years, a method for reducing a scattered-ray component and a noise component from the radial image by image processing has been proposed. U.S. Pat. No. 8,064,676 discloses a technique of reducing a scattered-ray component which is seen to be dominant in pixels of high luminance in a low frequency band and a noise component which is seen to be dominant in pixels of low luminance in a high frequency band in accordance with a frequency and a luminance value of a radiation image.
So-called noise includes quantum noise derived from statistical fluctuation in positions and density of X-ray photons detected by a radiation detector as a result of a random phenomenon of the X-ray photons. The quantum noise approximately correlates with the dose of radiation which has reached the radiation detector. In a method in which a scattered-ray component reduction process and a noise reduction process are individually performed in accordance with a frequency and a luminance value of a radiation image, accuracy of reduction of a noise component may be deteriorated since the correlation between an amount of a scattered ray which has reached a radiation detector and a generated noise amount is not taken into consideration.